Atrial Septal Defect

 

The heart is the pump that provides energy to the rest of the body. It is a powerful, muscular pump. The human body needs energy. This energy is provided by blood, which runs within arteries and veins. The fuel is in the form of chemicals and oxygen derived from the blood, and this is turned into energy for work. Waste materials produced in the body are dumped in the blood to be carried away and destroyed in other areas.

 

There are two kinds of blood vessels. Arteries carry "pure" or "red" blood from the heart to the other organs and veins bring back "impure" or "blue" blood to the heart to be purified. The heart pumps the blood to every part of the body It is a muscle. Heart muscle does not get tired. It is an efficient, never ceasing pump. In the heart, there are four chambers. The upper chamber is the atrium (two - one each to right and left). The lower chamber is called a ventricle (two - right and left). The circulation is the flow of blood in a particular pattern through the heart chambers, arteries and veins.

 

The veins carry the "impure" blood (or "blue" blood) to the upper heart chamber (atrium) on the right side where it collects until the atrium is full. This then flows into the right lower chamber (ventricle). The ventricle, unlike the atrium, is a powerful pump. Suddenly, and forcefully, it propels the blood into the pulmonary artery and carries the "impure" blood to the lungs. Air enters the lungs and mixes with the impure (blue) blood. Oxygen enters the blood and the impurities leave it. The blood is now "pure" or "bright red" as it leaves the lungs and comes back to the heart. But this time to the left upper atrium. It then passes into the left lower ventricle which is the strongest chamber of the heart. It is the part of the heart that will pump blood to the rest of the body.

 

The pressure that is produced in the left ventricle is similar to that in a garden hose when the water is turned on full-blast. So, when in the left ventricle, the blood suddenly gets a powerful thrust and enters the aorta - the largest and toughest artery in the whole body. The pure oxygenated blood carrying energy-giving nutrients is distributed to all organs of the body. Blood flows to every part of the body and so gets energy from the blood. So in summary impure blood from veins reaches the right atrium of the heart and flows to the right ventricle. From here, it passes through the pulmonary artery to the lungs, where oxygen is taken up, and wastes destroyed. Oxygenated blood reaches the left atrium, and then the left ventricle and is powerfully pumped into the aorta, from which it is directed to all the parts of the body.

 

Valves keep blood flowing in the same direction. The four valves in the human heart are one at each junction of two chambers. Between the right atrium and right ventricle there is the tricuspid valve (it has three leaves or 'cusps'). From the right ventricle blood is kept flowing towards the lungs by the pulmonary valve. In between the left atrium and left ventricle there is the mitral valve (looks like the bishop's 'mitre') and finally, at the junction of left ventricle and aorta, is the aortic valve. Both the aortic and pulmonary valves have 'cusps' or leaves that are half-moon shaped (semi-lunar valves). Blood from the left ventricle enters the aorta. The very first branches from the aorta are small "feeder" arteries (coronary arteries). These arteries turn back and run over the heart itself. There are two main coronary arteries, the right and left, which give rise to several smaller branches. These dive into the heart muscle and bring vital nutrients and oxygen to the heart. Using these nutrients, the heart can perform its pumping action.

 

The heart (muscle) has some special features. It is formed by millions of small cells (myocytes) and is made up of two types of protein - actin and myosin. These are the same two proteins of skeletal muscle. Using the energy from oxygen and nutrients they slide over each other which causes the whole muscle to shorten. The muscle cells are arranged in a circular pattern, like a ball or a balloon, so when the muscle shortens, the heart becomes smaller.

 

The two upper chambers of the heart (atria) are separated by a "wall", the atrial septum. Sometimes, this "wall" is not complete - there is a hole in it. This hole is known as an Atrial Septal Defect - or ASD and may be large or small, single or multiple. The heart may be normal in all other ways, or there may be other defects too. In the normal heart, blood flows into the right sided chambers (atrium and ventricle) and is completely separated from that in the left sided chambers, by the atrial septum. When there is a hole in this "wall", blood from the left atrium flows through the hole into the right side. This is due to the pressure of blood in the left atrium being higher than the right. The right (lower) ventricle receives blood from two places. The normal amount of "impure" blood coming from the veins through the right atrium and some extra blood through the hole in the atrial septum into the right ventricle.

 

So, the ventricle has to work harder to pump this increased volume of blood into the lungs and, as a result, the lungs receive a larger amount of blood than normal. When the lungs get more than the normal amount of blood, they become "flooded" and stiff. Breathing becomes difficult. When there is a lot of blood in the lungs, it does not flow quickly, and this causes a high risk of infections. Children with ASDs often catch a "chest cold" - maybe even several times a month. As many years go by, the right ventricle may become weak due to the constant hard work and will "fail" to pump out the blood entering it - heart failure. In most ASDs, these changes take many years to develop. Many children and young adults with an ASD are not even aware of it until they are 30 or even 40 years old. Frequent chest colds occur and if very severe, these may prevent normal growth and development of a child. Also, the lungs receive a large blood volume, which is harmful after some years. The blood vessels in the lung become hard and thick, and pressure inside them increases. Pulmonary hypertension. Pulmonary (lung), hyper (high) and tension for blood-pressure -  a very serious complication.

 

After several years, the ventricle may fail - heart failure. Another complication is arrhythmia - an irregularity in the rhythm of the heart. Since it handles a large volume of blood, the right atrium becomes enlarged and this causes a disturbance in the heart's electrical activity, causing it to beat faster - a disease called atrial fibrillation. All of these problems are common in large atrial septal defects, but another problem which may occur in both large and small ASDs is paradoxical embolism. Blood flow in the veins is normally slow and sluggish, and some small clots may form. Clots are small pieces of hardened blood inside a vein. In a normal person, these clots may pass through the heart into the lungs where they are "filtered" and prevented from entering the arteries along with the purified blood. When there is an ASD, however, the clot, on entering the right atrium, may pass across the ASD, into the left atrium. Along with the "pure" blood, it can then pass into the arteries, and from here to the brain. In the brain a clot may block a blood vessel, preventing blood flow to a part of the brain which can lead to stroke.

 

Stroke is an injury to the brain and may cause weakness or paralysis of an arm or leg, or the inability to speak or even unconsciousness. It can be a very serious problem and because of the risk of stroke it is advisable that even small ASDs be closed, by surgery or other methods.

 

Some types of ASD have other defects of the heart. The pulmonary veins carry pure blood from the lungs back to the heart and these normally connect with the left atrium. In one variety of ASD, these pulmonary veins may connect with the right atrium - a condition called anomalous (abnormal) drainage of pulmonary veins. In other types of ASD, the mitral valve may be abnormal. The wall between the lower chambers of the heart (ventricles) may also have a "hole" - ventricular septal defect (VSD). Any other birth defect of the heart may co-exist with an ASD which should, in most cases, be repaired (over 95% of doctors). Recently, a very few cardiologists are questioning this choice, but it is a very uncertain issue. Since most children with ASDs are totally without complaints, it is usual for an ASD to be detected only when the child is examined at school on a routine check-up, or while tests are being done for some other illness. Sometimes, it is detected only in young adulthood. Although there is no urgency, the closure should be done as soon as possible to avoid even the small risk of heart failure or paradoxic embolism. An operation is (preferably) avoided in very small children but ASDs can cause problems very early in life. One such instance is the ostium primum type ASD, which usually has other defects - like mitral valve clefts associated with it. These children may develop heart failure very soon and need surgery sometimes even within the first year of life.

 

The “medical curiosity” of closure without treatment is rare and most ASDs need to be closed surgically. Traditionally, closure is usually by operation. The hole in the atrial septum is stitched using a special thread mode of prolene or polypropylene (a type of polythene). When the ASD is very large, it may hove to be closed with a "patch" of material placed over it and stitched in place. This may be from the covering of the patient’s own heart - pericardium, A synthetic material like silk cloth or Dacron is also commonly used. When other defects occur additionally, the operation is a little more complex. When the pulmonary veins open into the right atrium, they must be redirected back to the left atrium. When the mitral valve is abnormal, it must be repaired, or in very rare instances, replaced with an artificial valve. Recently, some alternative methods have been tried. These are "experimental", in that their effectiveness in the long run has not been proved. The advantages with these new procedures is that they are less painful, make hospital stay shorter, and avoid a disfiguring scar of a surgical incision.

 

One of these is trans-catheter closure. A catheter is a special thin tube passed into the blood vessels through o small needle-stick in the groin or forearm. Through this catheter, o special device, similar to on umbrella, is passed into the heart. The "umbrella" device is pushed across the ASD and opened. The hole is now blocked by the umbrella, which is then fixed in place. Another method makes use of the idea of minimally invasive heart surgery  - see Port Access. Through 3 or 4 small "puncture" holes in the chest, specially designed instruments are passed into the chest and used to repair the ASD.

 

Surgery for ASDs is amongst the safest operations in cardiac surgery today. The mortality rate for ASD repair is below 1%. Major complications are uncommon but, rarely, bleeding may be excessive and blood transfusions are needed and a hospital stay is usually 5 days to a week.

 

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